INCREASED ANESTHETIC RISK

In: Anesthesia

20 Sep 2009

INCREASED ANESTHETIC RISK

Obesity, defined as a body mass index (BMI) greater than 30 kg/m2 of body surface area, is rampant in the United States. It is estimated that 4% of middle-aged men and 2% of middle-aged women have clinically significant obstructive sleep apnea (OSA) and that obesity is an independent causative risk factor in 60 to 90% of them. OSA is defined as a cessation of airflow for more than 10 seconds, in spite of continuous attempts to breathe, for 5 or more times per hour of sleep. Usually OSA is associated with snoring, and often produces at least a 4% drop in oxygen saturation of arterial blood. Unfortunately, it is estimated that between 80 to 95% of OSA patients are undiagnosed. Because only a relatively small percentage of OSA patients have craniofacial and orofacial abnormalities, or nasal or tonsil-related obstruction, we must be particularly suspicious of OSA in obese patients.

During OSA, the negative pressure created by the nasal obstruction causes the retropalatal pharynx, the retroglossal pharynx, and the retroepiglottic pharynx to collapse because the anterior and lateral pharyngeal walls have no bony support. In obese patients, increased fat deposition in the pharyngeal tissues decreases the size of the pharynx. The degree of fat deposition in the lateral pharyngeal wall correlates with the severity of the OSA. Additionally, the incidence and severity of OSA seems to correlate with the diameter of the neck. Cialis Jelly

During OSA, the patient becomes progressively hypoxic and hypercarbic, and there is ever-increasing respiratory effort which eventually stimulates the reticular activating system to arouse the patient from sleep. Once the patient awakens, the pharyngeal muscles regain their tone and the airway becomes patent. The resulting ventilation temporarily reverses the hypoxia and hyper-capnea and the patient then falls asleep, only to have the cycle repeat itself over and over throughout the night. OSA patients have poor quality of sleep and often fall asleep multiple times during the day, even when driving.

Preoperative examination of the awake patient’s oropharyngeal tissues when muscle tone is normal may not be representative of the same view once the patient is sedated and the muscle tone decreases. Preoperative, intraoperative, and postoperative sedatives and narcotics can reduce the muscle tone of the pharyngeal muscles and even cause pharyngeal collapse. They can alter the body’s ability to be aroused by hypoxia and hyper-capnea and may decrease the amount of respiratory effort, all of which may reduce the arousal mechanism necessary to awaken the OSA patient for cyclic breathing. If pharyngeal collapse occurs in the perioperative period, mask ventilation may be ineffective, and intubation, even by anesthesiologists, may be impossible. One large study demonstrated that failure to intubate by the anesthesiologist was 100 times more likely in an OSA patient compared to the general population. Additionally, because obese patients have a reduced functional residual capacity and higher metabolic oxygen consumption, they desaturate much faster than normal-sized individuals. viagra jelly online

For all these factors, dentists must use extreme caution in planning anxiety and pain control for obese patients who have or might have OSA. If sedation is chosen, supplemental oxygen provides a small but important safety cushion if difficulty arises. The drug selected should be given in small intravenous increments for a slow and careful titration. The drug should have a pharmacological antagonist in plain sight and therefore immediately available if needed. Since the IV is the patient’s lifeline if a respiratory crisis were to occur, only a catheter with a continuous flow of crystalloid will virtually guarantee that the lifeline will function in a life-threatening emergency. Although low-dose oral anxi-olysis is reasonably safe in the OSA patient, deeper levels of oral conscious sedation, and especially attempts to titrate with multiple stacked doses of oral sedatives, have a markedly reduced margin of safety. Also, there is no immediate route of administration to pharmacologically reverse the sedation if obstruction occurs. Deep sedation further increases the risk of irreversible obstruction in the OSA patient. Finally, selective nonsteroidal antiinflammatory analgesics for postoperative pain control are safer in this population than are narcotics. Patients with OSA can be very challenging to manage, but those who are undiagnosed are even more so. As the incidence of obesity continues to rise, dentists must be even more aware of the possible negative outcomes associated with sedation or anesthesia in this population and plan accordingly. The bottom line is that extra-large patients may not need extra-large doses, but in fact be quite sensitive to very small doses of CNS depressants. order lexapro


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Blog invites submissions of review articles, reports on clinical techniques, case reports, conference summaries, and articles of opinion pertinent to the control of pain and anxiety in dentistry.